There is known a reversible percussive action machine (cf. West German Pat. No. 2,340,751, published Aug. 11, 1973) comprising a housing accomodating a hammer capable of reciprocations under the action of a fluid under pressure, and a system for valving or distributing the fluid to assure that the hammer delivers impacts either on the front or head end, or on the rear or tail end of the housing to provide either for a forward travel of the machine or for backing up, respectively.
The distribution of the fluid under pressure both for the forward and rearward percussive actions of the machine is controlled by a fluid valving member connected movably to the hammer.
The fluid valving member may be fixed in place relative to the housing either in front or rear positions; in the front position the valving member controls the passage of the fluid to assure the forward percussive action, while in the rear position it controls the fluid distribution for the rearward percussive action of the machine.
The fluid valving member is connected to the housing through a pipe joined to a flange element. The flange is rigidly secured in the housing, and the fluid under pressure is fed to the pipe through a flexible hose connected to this pipe. The valving member is fixed relative to the housing in one of the two positions by means of two pairs of stops made on the pipe and adapted to alternately embrace the flange, and by a spring-loaded ball stop element disposed in the flange and connected to a cable or rope. The flange also has longitudinal grooves for the passage of the pipe stops therethrough.
In order to reverse the forward percussive action of the machine, it is necessary to terminate the supply of fluid under pressure. Thereafter, by pulling the cable the ball of the ball stop is released from the socket. The flexible hose is then twisted to turn the pipe a certain angle for the stops to assume a position in registration with the longitudinal grooves of the flange. It is then necessary to pull on the flexible hose without releasing the tension applied to the cable and thereby move the pipe axially so as to have the front pair of stops disposed on the opposite sides of the flange, whereupon the pipe is again turned a certain angle so that the ball of the spring-loaded ball stop would be in alignment with the socket in the pipe.
The cable is then slackened and the pipe (and, therefore, the valving member) is fixed in place between the front pair of stops by the spring-loaded ball relative to the flange and the housing.
When the supply of fluid under pressure to the machine is resumed, the hammer will execute reciprocations inside the housing to deliver impacts on the rear (tail) end thereof to cause the machine to move back away from the hole made.
For a switchover to the forward percussive action the fluid valving member is displaced in the aforedescribed manner.
The above machine has inherent disadvantages due to its structural complexity, difficulties in handling, and unreliable reversal because to reverse the percussive action of the machine it is necessary to make several operations simultaneously involving manipulations of the cable (applying tension thereto) and the flexible hose (twisting and pulling the hose). It is consequently difficult for a single operator to do the reversal operation. In addition, attempts to twist the pipe in long holes made in a loose soil may fail altogether.
Another disadvantage of the above machine resides in the lack of a mechanism providing for automatically setting the machine for the forward percussive action. Therefore, the operations associated with starting the machine to perform the forward percussive action are made manually.
In addition, the aforedescribed prior art construction fails to provide for a swift reversal from the forward travel to backing (for example, in an emergency). Such a reversal requires, along with other manipulations, to move the pipe forward axially, which is normally impossible to make by the flexible hose.
There is also known a reversible percussive action machine (cf. West German Pat. No. 2,633,251, published Apr. 14, 1977) comprising a housing accommodating a hammer reciprocating under the action of a pressurized fluid to deliver impacts on a front end of the housing during the forward percussive action and on the rear end of the housing for backing the machine out of the hole, and a fluid valving member to control the distribution of the fluid movably connected to the hammer and provided with means for fixing the valving member relative to the housing in two positions, viz. for the forward and backward travel of the machine inside the hole. The means for fixing the fluid valving member to move the machine forward has the form of a spring-loaded elastic annular insert (pin) capable of displacement relative to the valving member, this pin being secured in a socket made in the side wall of the valving member and having a section adapted to respond to the pressure exerted by the fluid to come into engagement with the housing and thereby axially fix in place the fluid valving member relative to the housing. This means for fixing the valving member during backing of the machine has the form of a stop element provided on the inner wall of the housing and serving to cooperate with a stop provided on the fluid valving member.
The housing is axially spring-loaded relative to the fluid valving member to ensure displacement of the valving member from a position in which it distributes the fluid to cause the rearward percussive action to a position for the forward travel of the machine.
In order to set the valving member to the front position and thus assure the forward percussive action of the machine, it is necessary that a fluid under pressure be supplied along a flexible hose to the machine, which fluid would act to exert pressure on the surface of the insert (pin) facing the interior of a high-pressure fluid line and move the insert toward the housing. This causes the elastic element to be released, and the side surface of the insert tends to come into engagement with the stop element of the housing, whereby the fluid valving member is fixed in a position corresponding to the forward percussive action of the machine.
Subsequent to feeding the pressurized fluid, the hammer executes reciprocations inside the housing to deliver impacts on the forward end thereof for the machine to move ahead in the ground and leave a hole behind.
In order to reverse the percussive action of the machine, it is necessary to terminate the supply of fluid under pressure, whereby the annular elastic element acts to displace the insert to the socket of the valving member, be brought out of engagement with the axial stop of the housing and assume a position ensuring mobility of the valving member relative to the housing. By pulling the flexible hose the valving member is displaced axially of the housing until the stops of the valving member engage the stops of the housing for the element exerting a spring-loaded action on the valving member relative to the housing to be compressed. Thereafter, without releasing the pull force from the flexible hose, the pressurized fluid is fed therethrough to the machine to provide for an axial force to be exerted on the valving member and directed toward the rear portion or tail end of the housing. This axial force acts to fix the valving member in a position that ensures the rearward percussive action of the machine. In this position the valving member provides for reciprocating motions of the hammer in the housing to deliver impacts against the rear part (tail end) of the housing for the machine to move in the hole in a reverse direction or backwards.
For a repeated switchover of the machine to the forward percussive action the supply of the pressurized fluid must be terminated. The element which spring-loads the valving member, relative to the housing acts to move the valving member to its front position corresponding to the forward percussive action of the machine for this valving member to be fixed relative to the housing under the action of the fluid supplied under pressure in the aforedescribed manner and the apparatus to execute the forward percussive action.
However, the just described apparatus has a rather low reliability because the means for fixing the valving member is susceptible to failure because the force transmitted to the insert (pin) by the fluid under pressure to push the insert from the socket and determined by the product of the pressure of the fluid by the cross-sectional area of the insert (pin) is small. This force must, however, be greater than the force produced by the annular elastic element. In consequence, the force produced by the annular elastic element is still smaller, while the annular elastic element should feature relatively small but constant power characteristics. It is known, however, that annular elastic elements are difficult to fabricate and offer no such stable power characteristics. Therefore, when the annular elastic element has a greater than rated rigidity, the force of the pressurized fluid fails to expel the insert, and the valving member fails to be fixed relative to the housing to make the machine produce a forward percussive action.
Conversely, if the elastic element is not sufficiently rigid, the insert (pin) would fail to be forced back into the socket of the valving member, and the valving member would fail to be moved axially from the housing to be fixed in a position corresponding to the reverse percussive action of the machine.
In addition, the annular construction of the elastic element overcomplicates the machine in that it becomes larger in diameter, which affects its specific power.
This machine is of low reliability also because its parts and units are susceptible to damage; the most susceptible are the annular elastic element, the fluid member and the housing in the location where the insert is accommodated. The damage may be caused due to rigid transmission of impact loads from one part to another.
Further, the machine is disadvantageous in that the insert (pin) bears on the axial stop by its side cylindrical surface, which causes high contact stresses and may result in failure of the housing or the insert (pin).